INDEX Abnormal conditions other than short circuits ith directionalcomparison pilot ying, A-c tripping, 335 with phase-comparison pilot relaying, Angle-impedance relay, 79 for tripping on 1088 of synchronism Broken-delta connection burden calculation 362 140 Angle of maximum torque, adjustment, for detecting grounds in ungrounded of power relays, 52, 55 for polarizing directionalground relay of shortcircuit relays. 55 Arcs, effect on distance relays, 345 resistance of capacitance potential devices, 302 135,140 Arc-furnace-transformer protection Buchholz relay, 281 270 Burden, current-transformer, 1 14 potential ASa accuracy classification,, of current transformer. 133 transformers. 121 Bus protection, automatic reclosing, 292 by of potential transformers, 193 back-up relays, 275, 291 Attenuation. carrier-current. 378 circuitbreaker by-psasing, 292 Automatic reclosing, see reclosing, combined power transformer and bus, 287 automatIc current differential with overcurrent relays Auxiliaries,, station, protection of, 229 278 current differential with overvoltage see also Motor protection relays, 288 current differential with Back-up relaying, defined, 6 284 directional effect of intermediate current sources comparison, 277 fault bus,, 275 grounding secondaries of differentially connected CT's for bus protection, 275, 291 291 partial-differential, 282 ring-bus,, 290 generator external fault, 227 testing, 292 voltage differential with linear reversed third zone. 175. 349 cou, 284 transformer external fault. 264. 268 with pilot relaying, 378, 386 Bushing potential device, see Capacitance Blind spot in pilot relaying, potential device Blinder with directional-comparison relaying 386,390 Capacitance potential device, broken burden Blocking pilot, 88, 91 140 comparison with instrument PTs, 144 Blocking terminal, with a-c wire-pilot relaying couplingcapacitor insulation coordination 142 effect of overloading, 138 NDEXI N D E X 1 Abnormal conditions other than short circuits,, 8 A-c tripping, 335 Angle-impedance relay, 79 for tripping on 1088 of synchronism, 362 Angle of maximum torque, adjustment,, 57 of power relays, 52, 55 of shortcircuit relays, 55 Arcs, effect on distance relays, 345 resistance, 302 Arc - furnace - transformer protection, 270 ASA accuracy classification,, of current transformers,, 121 of potential transformers, 133 Attenuation, carrier-current, 378 Automatic reclosing, see Reclosing, automatic Auxiliaries,, station, protection of, 229 see also Motor protection Back-up relaying, defined, 6 effect of intermediate current sources, 347 for bus protection, 275, 291 generator external fault,227 reversed third zone, 175, 349 transformer external fault, 264, 268 with pilot relaying, 378, 386 Blind spot in pilot relaying, 94 Blinder with directional-comparison relaying, 386, 390 Blocking pilot, 88, 91 Blocking terminal, with a-c wire-pilot relaying, 375 with directionalcomparison pilot relaying, 392 with phase-comparison pilot relaying, 383 Broken-delta connection, burden calculation, 140 for detecting grounds in ungrounded systems,, 320 for polarizing directionalground relays, 151 of capacitance potential devices, 135, 140 Buchholz relay, 281 Burden, current-transformer, 114 potential transformer, 133 Bus protection, automatic reclosing, 292 by back-up relays, 275, 291 circuitbreaker by-psasing, 292 combined power transformer and bus, 287 current differential with overcurrent relays, 278 current differential with overvoltage relays, 288 current differential with percentage relays, 284 directional comparison, 277 fault bus,, 275 grounding secondaries of differentially connected CT’s, 291 partial-differential, 282 ring-bus,, 290 testing, 292 voltage differential with linear cou, 284 Bushing potential device, see Capacitance potential device Capacitance potential device, broken burden, 140 comparison with instrument PT’s, 144 couplingcapacitor insulation coordination, 142 effect of overloading, 138 INDEX